1. Field of the Invention
This invention relates to the use of a self-lubricating layer for a data storage device, and more particularly to a silicon nitride self-lubricating layer for a data storage device.
2. Description of Related Art
Rigid disks with thin-film recording layers are a popular method for storing digital data. In a hard disk drive, a magnetic disk is installed on a spindle motor and driven to rotate. Hard disk drives utilize an actuator for positioning a read/write head over the spinning disk. The read/write head includes an electromagnetic transducer contained within an aerodynamic xe2x80x9cslider.xe2x80x9d In conventional hard drive systems, when the disk is stationary, the slider rests on the surface of the disk. When the disk is rotated at high speeds, an air bearing is formed beneath the slider, which supports the slider slightly above the surface of the disk. The slider and disk surface are typically made extremely smooth so that the slider is capable of flying very close to the disk surface without impacting protrusions on the disk surface.
One problem encountered with air bearing-based disk storage systems occurs when the disk first begins its rotation. When the disk is stationary, the slider experiences static adhesion, or stiction, with the disk surface, particularly when both the slider and disk surfaces are very smooth. Thus, when the disk begins its rotation, the stiction between the slider and the disk can result in damage to either or both the slider and the disk. In addition, in order for the slider to fly at low heights above the disk surface, there must be good lubrication between the slider and the disk. To avoid such damage, conventional magnetic disks are provided with a diamond-like carbon (DLC) overcoat for protection and a thin layer of perfluoronated polyether (PFPE) liquid lubricant, possibly mixed with a solvent, such as PF-5060, available from the 3M Corp. of St. Paul, Minn.
The deposition of the carbon protective overcoat and the liquid lubricant requires additional processing steps, which add to the complexity of the manufacturing process. After the carbon overcoat is sputter deposited over the recording layer, the lubricant layer is applied by immersing the disk in the liquid lubricant solution. The disk is then drawn out of the lubricant to produce a uniform liquid lubricant layer over the outer surface of the disk. After lubrication, the disk is then processed through a tape burnishing step, in which a very fine abrasive tape is used to burnish both sides of the hard disk to ensure particle removal and to reduce surface asparities.
Another popular method for storing data in computer-readable form is optical recording. As used herein, the term xe2x80x9coptical storagexe2x80x9d refers to all computer-readable data storage systems in which data is either written or read through the use of a laser. Various kinds of optical systems are known, including but not limited to compact disk read only memories (CD-ROMs), and erasable optical data storage systems, such as phase-change and magneto-optic (MO) systems. In typical optical systems, a laser beam is focused from an optical head to record data on the recording layer of an optical disk. A small spot is generated on the recording layer modulating, for example, the phase, intensity, polarization, or reflectivity of a readout optical beam which is subsequently detected by a detector in the optical head.
MO systems typically include a data storage disk having a substrate, a magnetic recording layer, and a protective overcoat. To record data, a small portion of the recording layer is heated by a laser beam, which enables the magnetization direction of the recording layer to be switched by application of an external magnetic field. In phase-change type storage systems, information is recorded onto a disk by utilizing a recording film which is rendered in an amorphous state when heated to a given temperature (for instance, about 600xc2x0 C.) higher than the melting point and then rapidly cooled and is recrystallized when heated to a temperature (for instance, about 400xc2x0 C.) lower than the melting point and then slowly cooled. Recorded information is reproduced by utilizing the fact that the reflectance of light in the amorphous state is different than in the crystal state. In typical optical and MO systems, the laser can heat the desired recording portion to temperatures of 400xc2x0 C. and above.
Conventional optical and MO data storage systems utilize a suspended read/write head which is mounted above the disk surface at distances of over 20 micro-inches (xcexcxe2x80x3). Because of the large distance between the read/write head and the recording layer in such xe2x80x9cfar fieldxe2x80x9d suspended head systems, the recording spot size is large and, accordingly, the recording density is poor. Recently, however, there has been development in the use in optical storage systems of air bearing-supported read/write heads, similar to the flying sliders in magnetic hard disk drives. The use of sliders enables the read/write head to be brought much closer to the disk surface, thereby improving the recording density. In conventional hard disk drives, the read/write head may be supported by the air bearing at a distance of approximately 20-30 nm from the disk surface.
Present data storage disk systems present numerous disadvantages. The deposition of the carbon overcoat for protection and a PFPE liquid layer for lubrication requires multiple steps and multiple layers in order for the read/write head to effectively fly close to the disk surface. The solvents used for liquid lubrication are expensive and may be environmentally hazardous. In addition, liquid lubricants are not thermally stable and can be evaporated by exposure to high heat. In optical and magneto-optical recording, in which the laser in the read/write head can create extremely high localized temperatures, depletion of the lubricant layer through evaporation can result in a significant degradation in performance.
Other types of non-rotating data storage devices may also be read from and written to with slider read/write heads, and thus experience the same problems as found in rotating disks. For example, smart cards, which are credit card-type storage devices, include a rectangular shaped strip that serves as the storage medium, and use read/write heads that move over the surface of the storage medium in a linear fashion. Similar to rotating disks, an air bearing is formed to support the slider. Non-rotating data storage devices have similar lubrication requirements as found in traditional hard disk drives.
Accordingly, there is a need for an improved system for storing data on a data storage device, which provides good, reliable lubrication and does not require additional complex processing steps.
In accordance with the invention, a method of operating an electronic data storage device comprises providing a data storage disk, said disk comprising a substrate, a recording layer deposited over said substrate, and a silicon nitride self-lubricating layer deposited over said recording layer, and rotating said disk to create an air bearing to support a slider, wherein said silicon nitride self-lubricating layer provides lubrication between said disk and said slider.
In accordance with another aspect of the present invention, a disk for use with a slider that is supported by an air bearing comprises a substrate, a recording layer deposited over said substrate, and a silicon nitride self-lubricating layer deposited over said substrate and forming an upper surface of said disk, said silicon nitride self-lubricating layer providing lubrication between said slider and said disk when said slider contacts said disk.
In accordance with another aspect of the present invention, an apparatus comprises a disk comprising a substrate, a recording layer deposited over said substrate, and a silicon nitride self-lubricating layer forming an upper surface of said data storage disk, a slider supported by an air bearing created by rotation of said data storage disk, and an actuator for positioning said slider.
In accordance with another aspect of the present invention, a data storage device for use with a slider comprises a substrate, a recording layer deposited over the substrate, and a silicon nitride self-lubricating layer deposited over the recording layer to form an upper surface on the recording layer. The silicon nitride self-lubricating layer provides lubrication between the recording layer and a slider. In one embodiment, the data storage device has a memory strip, wherein the memory strip includes the substrate, recording layer and the silicon nitride self-lubricating layer. The data storage device may include a second substrate with a slot that the memory strip is removably stored in. In another embodiment, the memory strip is positioned on the exterior surface of a second substrate. The memory strip may be deposited over only a portion of the substrate. Thus, for example, where the data storage device is a credit card-type storage device, the substrate may be the card itself, and the recording layer and the silicon nitride layer may be deposited as a strip over a portion of one of the side of the card. In another embodiment, a plastic polymer is deposited over the substrate and the recording layer is deposited over the plastic polymer. The recording layer may be an iron oxide material, which when deposited over a plastic polymer is particularly advantageous because of the low temperature associated with the deposition process of the iron oxide material.
In accordance with another embodiment of the present invention, a method of manufacturing the data storage device includes providing a substrate, depositing a recording layer over the substrate and depositing a silicon nitride layer over the recording layer, such that the silicon nitride layer forms an upper surface on the recording layer. A plastic polymer may be deposited over the substrate and the recording layer is deposited over the plastic polymer. As described above, the recording layer may be an iron oxide material. The silicon nitride layer may be sputter deposited, for example using direct-current reactive sputtering. The process of sputtering the silicon nitride includes introducing nitrogen and argon gas into the sputtering chamber. The ratio of nitrogen and argon may be between approximately 3.3 to 6.7. The substrate, recording layer, and silicon nitride layer may form a memory strip used, e.g., on a credit card-type storage device.
In another aspect of the present invention, a data storage device for use with a slider includes a substrate, a plastic polymer layer deposited over the substrate and an iron oxide recording layer deposited over the plastic polymer. The data storage device may also include a silicon nitride self-lubricating layer deposited over the recording layer to form an upper surface over the recording layer. The data storage device may include a memory strip that is comprised of the substrate, the plastic polymer and the recording layer. The memory strip may be stored in a second substrate or mounted on the exterior of a second substrate. Alternatively, the plastic polymer layer and the recording layer may be deposited over only a portion of the substrate.